Thursday, January 8, 2009

Air Dryer

Compressed Air Dryer

Two common types of dryers are refrigeration and adsorption (desiccant). When choosing a dryer, a general rule is to first select a pressure dew point that meets the requirements of the application and is 15° to 20° below the plant's lowest ambient conditions.

(A dryer's efficiency is measured as the dew point, which is the level of dryness in a compressed air system.)

Dew point determines the major difference for selecting either refrigeration dryers or desiccant models.

Refrigeration dryers cool air to a pressure dew point of 2 to 10°C, which is the effective limit on this type of dryer, as water freezes at 0° C. This style is ideal for general industrial applications in light assembly, including those that use air motors, air tools, valves, cylinders and rotary actuators, and painting and welding equipment.

When piping is installed in ambient temperatures below the dryer dew point (i.e., systems with outside piping), refrigeration dryers are not suitable.

Adsorption dryers pass air over a regenerative adsorbent material that strips moisture from the air. These types of dryers are extremely efficient and can provide a pressure dew point at 7 barg as low as -40° C. Desiccant dryers remove liquid from the compressed air system through the use of chemical beds.

A portion of the dried air is usually drawn off, passed through the chamber being regenerated, and discharged to atmosphere.